It is well known to attach a variety of rigs such as hydraulically operated rigs above a wellhead. For example, snubbing units are known in the oil and gas industry for facilitating access to a well which is under pressure including, for example, well operations such as well completions. A snubbing unit includes structure and equipment above a wellhead for manipulating tubular components such as pipe, tubing, and bottom hole assemblies (BHA) in and out of a well while controlling the well under pressure. Wellhead components are not conventionally equipped to deal with the manipulation of tubular components therethrough. Therefore, additional equipment in cooperation with the snubbing unit provides additional sealing and physical handling components which are required to handle tubular components, which may be either heavy tubular components which tend to fall into the well, termed “pipe heavy”, or which can be upwardly energized for ejection from the well under pressure, termed “pipe light”.
Snubbing units are either rig-mounted or stand alone units. Generally, a stand alone snubbing unit is supported on a structure that is in turn supported from the wellhead. A wellhead comprises structure which provides the interface between fluids in the well, the surface equipment and the environment. Wellhead integrity is critical. Wellheads include blowout preventors (BOPs) and other fluid-control devices, the success of which depends on the integrity of the wellhead. Conventionally, the snubbing structure places significant loading on the wellhead which is not related to its primary task of containing well fluids. Loading includes vertical gravity loads, working loads and lateral wind loading.
Threaded wellhead connections, such as casing bowls that are screwed to the casing, are particularly vulnerable to bending loads imposed on the wellhead. Additional aspects that contribute to loading on the wellhead include difficulties with proper leveling of the snubbing unit.
There is, therefore, a need in the art for an improved load bearing support for rigs above a wellhead such as a snubbing unit.